The proposed research includes four projects. The first project involves completion of a comprehensive summary and functional analysis of the afferent connectivity of the somatosensory portions of the cat's mesencephalon and diencephalon. The second project involves completion of a similar analysis of the monkey's diencephalon and mesencephalon as well as of it's inferior olive. The studies will be performed at the light microscopic level using a differential orthograde labeling strategy in which autoradiographic and degeneration tracing methods are combined in the same preparation. The third project is to study the relationship between the patterns of afferent input to certain parts of the cat's thalamus and the efferent projections from these parts to the cerebral cortex. This study will be performed using a triple labeling strategy in which retrograde labeling methods (horseradish peroxidase) are added to the differential orthograde labeling procedures. The fourth project is a light microscopic autoradiographic study of possible differences in the incorporation of various precursors by proteins of different types of cells in the dorsal column nuclei of cats. The effects of certain variables on these incorporation patterns (e.g., the ionic composition of the solution in which the precursor is dissolved) will also be studied.